The invention concerns a drive unit, and more particularly concerns a drive unit having a housing, gearing, shaft, actuator, and slip clutch.
In the case of a conventional drive unit of the usual type, there is provided an electric motor with a multi-step, RPM reducing drive enclosed in one housing. Between a drive shaft from the stepped down transmission and a driven component designed as a rotary actuator, a slip clutch is inserted which is comprised of several disks, i.e., a disk clutch. The disks are pressed together by a screw compressed spring, which, on the one side presses against the disks, and on the other side against the head of a screw, which is threadedly engaged in the drive shaft facility.
Motor-gear drive-units of this kind are installed for the activation of external mirrors on motor vehicles and particularly on trucks. The slip clutch is necessary so that the motor vehicle mirror, which is usually positioned by the motor driven actuator, can be also set by hand. The step-down gear drives are, naturally, self limiting.
The sliding moment, by the overstepping of which the frictional connection of the slip clutch is overcome, is not exactly defined, but varies within a non-reproducible range. In the case of a rotary movement contrary to the normal rotation, the screw will loosen itself, whereby the clutch will fail to hold. Moreover, there is a high cost of installation related to the many parts which must be handled.